EXAMPLE
- Predicting Ion Charge:

Predict the charge or charges for the ions formed by atoms of (a)
scandium, Sc, (b) gallium, Ga, and (c) sulfur, S. Write an abbreviated
electron configuration for each ion and use it to explain why the ion
acquires the charge it does.

Solution:

a. Because scandium is a metal in group 3 on the periodic table, we expect
its atoms to lose three electrons each and form +3 cations with the stable 3s23p6
configuration of argon.

ScSc3++3e-

[Ar] 3d1
4s2[Ar] or [Ne] 3s2 3p6

b. Gallium is a metal, so we expect it to form cations. It is in
group 13, so we follow the guidelines for cations other than Al3+ and
those in groups 1, 2, or 3. The first step is to write the abbreviated electron
configuration for an uncharged gallium atom. The noble gas preceding gallium on
the periodic table is argon. Gallium atoms can lose one electron to form Ga+
ions with the stable 3d104s2 configuration.

GaGa++e-

[Ar]
3d10 4s2
4p1[Ar]
3d10 4s2

Gallium atoms can also lose three electrons to form
Ga3+ ions with the stable 3d10 configuration.

GaGa3++3e-

[Ar]
3d10 4s2
4p1[Ar] 3d10

c. Sulfur is a nonmetal, so we expect its atoms to gain electrons and form
anions. Each atom gains two electrons to form a S2- ion with the
stable, noble gas electron configuration of argon.